Conformance improvement by polymer gel treatment is a common practice to improve oil recovery from a heterogeneous hydrocarbon-bearing reservoir. When a gel solution that includes a water-soluble polymer and cross-linker is injected through injection wells, gel will be formed in the hydrocarbon reservoir after a certain time. As a result, any subsequent injection water will be diverted to un-swept or less-swept regions of the formation. In water shutoff applications, a gel may be injected through one or more production wells to block or reduce unwanted excess water or gas production or both.
When a gel solution solidifies inside reservoir rock, pore sizes of the rock will be reduced and the pore throats will be clogged. There will be, therefore, a reduction in the regional permeability where the gel invades, and the flow diverting or blocking purpose is then achieved. But after a certain time, gel may undergo syneresis and release water out of the gel system. The rate of gel syneresis may depend on the specific gel composition and usually accelerates with an increase in temperature. Gel strength is greatly reduced and rock permeability will gradually restore.
Coreflooding experiments have been used to measure the permeability variation for gel performance evaluation, but injection pressure may be a detriment in gel strength or integrity. Also, coreflooding is time consuming, and a long term evaluation may take months. Coreflooding may also cause some safety concerns if the coreflooding system is kept at high pressure (for example, greater than 3,000 psi) and high temperature (for example, greater than 220° F.) conditions for a lengthy duration of time.